This invention relates to the field of optimizing tire uniformity, and more particularly to a method of adapting the warm-up cycle of a force variation machine for each tire to stabilize the measurement perimeters and optimize the warm-up cycle to provide accurate data and maximize utilization of the force variation machine.
In the art of manufacturing pneumatic tires, rubber flow in the mold or minor differences in the dimensions of the belts, beads, liners, treads, plies of rubberized cords, sometimes cause non-uniformities in the final tire. When non-uniformities are of sufficient magnitude, they will cause force variations on a surface, such as a road, against which the tires roll and thereby produce vibrational and acoustical disturbances in the vehicle upon which the tires are mounted. Regardless of the cause of the force variations, when such variations exceed the acceptable minimum level, the ride of a vehicle utilizing such tires will be adversely affected.
The effects of non-uniformity are best explained by noting that several types of forces, which are of particular importance in the present application, are simultaneously exerted by a tire during its rotation under load against a surface. For example, radial run-out is an intrinsic tire non-uniformity best described as the xe2x80x9cout of roundnessxe2x80x9d of the tire. Also radial forces are exerted in the radial direction of the tire, or in a direction perpendicular to its axis of rotation and non-tangential to the road surface. Additionally, lateral forces are exerted in the axial direction of the tire or in a direction parallel to its axis of rotation.
In a non-uniform tire, the radial run-out, the radial forces, and the lateral forces exerted by the tire will vary or change during its rotation. In other words, the magnitude and/or direction of the radial run-out, and the radial and lateral forces exerted by the tire will depend on which increment of its tread is contacting the surface.
The variations in radial and lateral force during rotation of a tire are usually caused by differences in the stiffness and/or geometry of the tire about its circumference or tread centerline. If these differences are slight, the radial and lateral force variations are considered insignificant and their effects unnoticeable when the tire is installed on a vehicle. However, when these differences reach a certain level, the radial and/or lateral force variations may be significant enough to cause rough riding conditions and/or difficult handling situations.
Consequently, methods have been developed in the past to correct for excessive force variations by removing rubber from the shoulders and/or the central region of the tire tread by means such as grinding. Most of these correction methods include the steps of indexing the tire tread into a series of circumferential increments and obtaining a series of force measurements representative of the force exerted by the tire as these increments contact a surface. This data is then interpreted and rubber is removed from the tire tread in a pattern related to this interpretation. These methods are commonly performed with a force variation machine which includes an assembly for rotating a test tire against the surface of a freely rotating loading drum. This arrangement results in the loading drum being moved in a manner dependent on the forces exerted by the rotating tire whereby forces may be measured by appropriately placed measuring devices. In a sophisticated tire uniformity machine (TUM) also known as a force variation machine (FVM), such as a Model No. D70LTW available from the Akron Standard Co. of Akron Ohio, the force measurements are interpreted by a computer and rubber is removed from the tire tread by grinders controlled by the computer. Examples of these methods are disclosed for example in U.S. Pat. Nos. 3,739,533, 3,946,527, 4,914,869, and 5,263,284.
In the past, force variation machines incorporated an adaptive warm-up cycle which is a method of adapting the Force Variation machine for each tire through real time data analysis of radial force, lateral force, radial first harmonic and phase angle. The warm-up period of the machine increases or decreases, depending upon the stabilization of these measurement parameters. The adaptive warm-up is intended to optimize the tire warm-up cycle to provide accurate data and maximum utilization of the equipment.
Current warm-up control methodology on Force variation machines consists of a fixed time function which initiates at the start of the tire loading sequence or after the loading of the tire is completed. At the completion of the fixed time warm-up, data is acquired and the machine cycle then advances to the next programmed step.
It has been found that the majority of tires will stabilize and warm up within the fixed time allowed. In some cases, tires require an extended amount of time to stabilize because of a varying number of circumstances. Often, however, the tires will stabilize in less than the allocated static warm-up time which results in under utilization of the Force variation machine.
It is an object of the present invention to provide a warm-up cycle for a force variation machine to obviate the problems and limitations of the prior art methods. Other objects of this invention will be apparent from the following description and claims.
In accordance with the invention, there is provided a first embodiment of a method for incorporating an adaptive warm-up cycle to a force variation machine for each tire being tested. The method includes the steps of rotating a tire mounted on the force variation machine in a first direction for two successive revolutions. Then the data values for the measured parameters are calculated for each of the two successive revolutions and the difference between the calculated data values for each of the corresponding measured parameters are compared with preset tolerance values. If the difference between the data values of each corresponding parameter is less than the preset tolerance values, the tire is graded with the data values of each parameter measured during the second revolution. Otherwise, the tire is rotated for additional revolutions in the first direction until the difference between the data values for the measured parameters measured during the second and third revolutions and so on are less than the preset tolerance values. Next, the tire is rotated in a second opposite direction and the steps are repeated. The tire being tested is graded with the data values of the measured parameters from the last revolution of the first and second opposite directions and the force variation machine is operated as needed.
Further, in accordance with the invention, there is provided a second embodiment of a method for incorporating an adaptive warm-up cycle to a force variation machine for each tire being tested. The second embodiment differs from the first embodiment in that the tire is rotated in a first direction for three successive revolutions and the data values for the measured parameters are measured for each of the three successive revolutions. Then, the difference between the calculated data values for each corresponding measured parameter measured during the first two successive revolutions are compared with the preset tolerance values. If the difference between data values of each corresponding parameter measured during the first two successive revolutions is less than the preset tolerance values, the data values of each parameter measured during the second revolution are used for grading the tire. Otherwise, the tire is rotated for a fourth revolution while the difference between data values of each corresponding parameter measured during the second and third revolutions are compared with the preset tolerance values while calculating the data values for the measured parameters from the fourth revolution. This continues with successive revolutions until the difference between the corresponding data values for the parameters measured during any two successive revolutions is less than the preset tolerance values. The adaptive warm-up cycle continues by repeating the steps while the tire is rotated in a second opposite direction. The tire being tested is graded with the data values of the measured parameters from the last revolution of the first and second opposite directions and the force variation machine is operated as needed. Also, in accordance with the invention, there is provided a third embodiment of a method for incorporating an adaptive warm-up cycle to a force variation machine for each tire being tested.
The third embodiment differs from the first and second embodiments in that the tire is rotated in a first direction for four revolutions in a first direction and the average of the data values for each parameter for the four revolutions of the tire are compared with the date values of the corresponding parameters during the fourth revolution of the tire. If the difference between the average data values and the data values of the fourth revolution are less than the preset tolerance values for each parameter, the tire is considered to be warmed up and the machine cycle continues. However, if the difference between the average data values for each parameter and the data values for the corresponding parameters calculated from the data generated during the fourth revolution is more than the preset tolerance values, the data values for each parameter for the next four revolutions in a first direction are calculated. Then, the data values from the eighth revolution are compared with the data values from the average of the data values for each parameter from the fourth to eight revolution. This process continues until these comparisons show that the parameters are not changing significantly, i.e., are less than the preset tolerance values. The adaptive warm-up cycle continues by repeating the steps while the tire is rotated in a second opposite direction. The tire being tested is graded with the data values of the measured parameters from the last revolution of the first and second opposite directions and the force variation machine is operated as needed.